The present invention relates to a magnetic recording medium suited to a high density magnetic recording, more particularly, a magnetic coated recording medium and also relates to a method of manufacturing the same.
Hitherto, the properties of a magnetic recording medium are defined by the film thickness .delta., coercivity H.sub.c, residual saturation magnetization M.sub.r and squareness M.sub.r /M.sub.s (M.sub.s : saturation magnetization) of the medium. See pages 1-15 of technical data MR 67-18 (1967) of the Society for Research of Magnetic Recording in Inst. of Electro. and Commun. Eng. of Japan. However, it does not necessarily follow that magnetic recording media having the same value in each of the parameters of H.sub.c, M.sub.r and M.sub.r /M.sub.s exhibit the same write/read characteristics when the writing in and reading from their media are made by use of the same head. For such circumstances, IEEE trans. Magnetics, MAG-20, pp. 81-83 (1984) has proposed indexes S*, S', .DELTA.h.sub.c, and .DELTA.h.sub.r. Here S* is the gradient at coercivity in magnetization curve, S' is the gradient at remanent coercivity in remanent magnetization curve, .DELTA.h.sub.c is so called switching field distribution, that is, half width of a differential magnetization curve normalized by the coercivity, and .DELTA.h.sub.r is so called residual switching field distribution, that is, half width of a differential residual magnetization curve normalized by the residual coercivity. But, even if such a new parameter is used, a sufficiently good correspondence cannot be obtained between the properties of a recording medium and the read/write characteristics thereof, especially, an output E.sub.o at a low density and a recording density D.sub.50 which provides an output of the half of E.sub.o.
As another parameter of the medium is the magnitude H.sub.s of an applied field with which the magnetization upon increase of the applied field and the magnetization upon decrease of the applied field begin to coincide with each other (or begins to separate from each other) in a main magnetization curve. However, only the correlation of H.sub.s with a magnetic motive force has hitherto been considered, as is discussed in pages 1-15 of technical data MR 67-18 (1967) of the Society for Research of Magnetic Recording in Inst. of Electro. and Commun. Eng. of Japan mentioned above.
The definition of each of the above-mentioned parameters is illustrated in FIG. 1a or 1b. In FIG. 1a, the ordinate represents the magnitude of the magnetization of a medium and the abscissa represents the magnitude of an applied field. In FIG. 1b, the ordinate represents the magnitude of a reproduction output and the abscissa represents the recording density.
Because of a lack of enough grasp of parameters corresponding to the write/read characteristics, the above-mentioned prior art cannot give a complete guide to what medium should be used in order to attain a high density magnetic recording.